See Overwatch Forums and https://www.reddit.com/r/OverwatchUniversity/comments/aatezy/why_match_quality_is_frequently_poor/.
Pay no mind to MHz. If you pay attention to him for any length of time, you will note that he lies constantly and gaslights anyone who calls him out on it.
Also see How Competitive Skill Rating Works - Season 17 and references, though I’m currently rewriting it for Season 18.